# How to simulate damage by reducing tower stiffness?

**URL:** <https://forums.nlr.gov/t/how-to-simulate-damage-by-reducing-tower-stiffness/8587>\
**Category:** Computer-Aided Engineering Software Tools\
**Created:** [April 1, 2025, 12:18pm UTC](https://forums.nlr.gov/t/how-to-simulate-damage-by-reducing-tower-stiffness/8587 "2025-04-01T12:18:27Z")\
**Posts on this page:** 1\
**Showing post:** 17

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**Author:** ![Jason.Jonkman](https://dub1.discourse-cdn.com/nrel/user_avatar/forums.nlr.gov/jason.jonkman/32/3086_2.png) [@Jason.Jonkman](https://forums.nlr.gov/u/Jason.Jonkman)\
**Post date:** [April 10, 2025, 2:56pm UTC](https://forums.nlr.gov/t/how-to-simulate-damage-by-reducing-tower-stiffness/8587/17 "2025-04-10T14:56:00Z")

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Dear @Meng.He,

Here are my responses:

1. Looking at Pietro Bortolotti’s GitHub repository for the BModes model of the IEA Wind 15-MW RWT: [IEA15\_BModes/RNAon at master · ptrbortolotti/IEA15\_BModes · GitHub](https://github.com/ptrbortolotti/IEA15_BModes/tree/master/RNAon), I see that his tower top-properties differ from yours, so, how did you obtain your values? Pietro’s model is for a cantilevered tower (`hub_conn` = 1), so, Modes 1 and 2 are the first side-side and fore-aft bending modes shapes and are a reasonable natural frequency (not Modes 6 and 7, which are higher modes).
2. When calculate the tower mode shapes in BModes for a floating system, `hydro_M` should be the added mass matrix, `hydro_K` should be the hydrostatic stiffness weight (accounting both for buoyancy and full-system weight), and `mooring_K` should be the mooring system stiffness.
3. You should be able to interpret the modes by plotting the shapes and by their natural frequencies, assuming that you have a reasonable idea what modes to expect (surge, sway, heave, roll, pitch, yaw, tower-bending, etc.)
4. `sec_loc`, `mass_den`, `flp_stff`, and `edge_stff` in BModes should match `HtFract`, `TMassDen`, `TwFAStif`, and `TwSSStif` in the ElastoDyn tower file. The other values in the BModes tower file (`str_tw`, etc.) should be set to to ensure they don’t have an effect on the solution, e.g., as I describe in the following forum topic: [Consistency between Bmodes and MBC](https://forums.nlr.gov/t/consistency-between-bmodes-and-mbc/1176).

Best regards,

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